A pipeline is constructed of pipe sections or pipe lengths which are welded end to end in the field as the pipeline is constructed. The ends of the pipes to be welded must be clamped in close proximity for welding, a task which is complicated as the pipes are commonly out of round and have high and low sections which resist alignment. It is desirable to true the ends before welding. However, on small pipe with heavy walls, e.g., 24" diameter pipe with 1" wall thickness, it is difficult to generate the force required to round the pipe.
Internal pipe clamps have been developed for clamping the pipes for welding and attempting to true the ends to be welded, such as disclosed in U.S. Pat. No. 3,937,382 to Cunningham et al. issued on Feb. 10, 1976, which have two sets of extendable clamps extendable to clamp to the interior surface of the pipes near the abutting ends of the pipe to be welded. The extendable clamps act to force the pipe into a more circular configuration for welding. However, even after clamping it is common to have pipes of different ovalities and slightly different diameters.
The welding is typically conducted by a welding device exterior the abutting pipes. It is desirable to provide a back up ring on the inside surface of the pipes at the weld. U.S. Pat. No. 3,937,382 discloses a back up ring of this type. Also, U.S. Pat. No. 4,556,162 issued to Gwin et al. on Dec. 3, 1985 discloses a internal pipe clamp with arcuate back up ring segments mounted on certain of the clamping members.
However, a need still exists for a more effective pipe clamp with a back up ring. The clamp should be capable of accommodating the mismatch between pipe ends and be capable of rapid deployment and capable of providing effective clamping.